This disclosure presents various embodiments of an electrolyte membrane for a reformer-less fuel cell. The fuel cell receives an oxidizable fuel (e.g., hydrogen or a carbonaceous fuel, such as Methane) from a fuel supply at a fuel manifold and air from an air supply at an air manifold. The electrolyte membrane conducts oxygen in an ionic superoxide form when the fuel cell is exposed to operating temperatures above the boiling point of water and below 500° C. to electrochemically combine the oxygen with the fuel to produce electricity. In various embodiments, the electrolyte membrane includes a porous substrate and an ionic liquid.
Fuel cells hold a great promise for the distributed generation of electricity. Since fuel cells can operate at higher thermodynamic efficiency than simple cycle turbines, the impact on greenhouse gas reduction is significant. Local & distributed generation by fuel cell does not suffer from the 7-10% transmission loss as observed with centralized electricity generation. In addition, distributed generation offers the society resilience against natural calamities, cyber-attacks and terrorist attacks which can incapacitate central generation plants and leave large populations helpless.
There is a significant debate whether variable energy resources (VER), such as wind and solar can continue to be integrated into the main grid beyond a certain fraction of the total load, due to their unpredictability. Many energy operators have already started complaining about such unpredictability and are questioning the ability to integrate more VERs into their grid. Fuel cells as distributed generators offer an excellent alternative to such problems. While as distributed generators, fuel cells provide local power, they also pump energy into the grid on demand, thus being a balancer of loads, and would, in addition, allow more VERs to be integrated to the grid.
Almost all fuel cells work with hydrogen as a fuel, however hydrogen itself is not a natural fuel. Hydrogen is usually obtained by steam reformation of hydrocarbons. The reformation spends a significant amount of energy, resulting in a reduced net thermodynamic efficiency and higher system cost. Natural gas has been explored heavily and successfully in the United States, and is likely to be the commercial fuel of choice for several decades to come. It is therefore desirable that fuel cells run on natural gas, i.e. methane, directly as opposed to reformed Hydrogen.
There are two predominant classes of fuel cells in commercial production, proton-exchange membrane fuel cells (PEMFC) and solid-oxide fuel cells (SOFC). Both are relatively mature technologies but suffer drawbacks that have prevented their widespread use. They work in the range of 25-100 C and 700-1000 C, respectively.
PEMFCs are proton (hydrogen-ion) conducting fuel cells, whereas SOFCs are oxygen-conducting fuel cells. Therefore, while PEMFCs must use a reformer to run on natural gas, oxygen-conducting fuel cells, such as SOFCs have the potential to run on both, hydrogen and hydrocarbons, i.e. methane. With reference to FIG. 1, the ion transport in hydrogen-conducting membranes versus oxygen-conducting membranes is shown.
PEMFCs, due to the need for reformers, are economically and energetically inefficient. Since PEM membranes work only in the hydrated form, and copious amount of water is produced as a result of the reaction, water management on both the sides of the cell is a difficult issue. Other problems such as catalyst drowning and destruction of carbon support due to water starvation occur. Additionally, the presence of COx, NOx and SOx in the fuel or air stream imparts a poisoning effect on the catalysts. Therefore additional infrastructure, such as chemical scrubbing, is required to reduce or eliminate such impurities, thus reducing the economical and energy efficiency advantages.
SOFCs have the potential to use natural gas directly, because they operate at very high temperature and conduct Oxygen. However, most practical and commercial SOFCs must use a steam reformer to perform as needed. They typically use a doped Yttria-stabilized-Zirconia (YSZ) as the oxygen conducting membrane. At high temperatures (800 C on average), serious issues arise, such as (a) catalysts, e.g. Ni and NiO cannot adhere on the membrane over several thermal cycles due to a mismatch of coefficient of thermal expansion (CTE); (b) commercial plastics and commercial metals, such as aluminum and common steel cannot be used, necessitating expensive metal and ceramic structural components; (c) gas fittings and controls become inordinately expensive to operate at the high temperatures. Operating at such high temperatures includes materials reliability and safety issues.
Many fuel cells work with hydrogen as a fuel, but hydrogen does not occur naturally with high abundance. It is usually obtained by steam reformation of hydrocarbons, which is inefficient and costly. It is therefore desirable that fuel cells use natural gas (primarily methane) directly as opposed to reformed hydrogen. New types of alkaline, acidic and molten salt electrolytes are being researched. However, with these technologies, the research is in the hydrogen ion (proton) conducting electrolytes and would require the fuel supplied to an ITFC would have to be hydrogen, and a reformer would be required to generate hydrogen from methane or other carbonaceous fuels.